1. Field
Aspects of embodiments according to the present invention relate to a flat panel display, and more particularly, to an organic light emitting display.
2. Description of Related Art
Recently, various flat panel displays (FPDs), with reduced weight and volume compared to that of cathode ray tubes (CRTs), have been developed. The FPDs include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and organic light emitting displays.
Among the FPDs, the organic light emitting display has self-emission elements that emit light from phosphors by re-combination of electrons and holes. The organic light emitting display is divided into two categories, a passive matrix organic light emitting display and an active matrix organic light emitting display.
In the active matrix organic light emitting display, a plurality of pixels are arranged in a matrix. Emission of the pixels is controlled using switch elements such as thin film transistors (TFTs) in the pixels. Display is performed through scan lines that select the pixels, data lines for controlling the emission of the pixels, and pixel power lines VDD for supplying voltage (or current) to the pixels.
Ideally, the pixel power lines VDD supply uniform voltage to the plurality of pixels coupled to them. Voltage values applied through the pixel power lines should be equal to each other in terms of the coupled pixels. However, this can be difficult to achieve due to an IR drop (e.g., a voltage drop) generated by the pixel power lines. That is, the voltages supplied to the pixels are reduced due to the IR drop as the distance that the pixels are from an external power supply increases. This is more clearly described with reference to FIG. 1.
FIG. 1 is a block diagram illustrating the structure of a conventional organic light emitting display.
Referring to FIG. 1, the organic light emitting display includes an image display unit 10 for displaying an image, a data driver 20 for transmitting data signals, and a scan driver 30 for transmitting scan signals. In addition, the image display unit 10 includes a plurality of pixels 11 including light emitting elements and pixel circuits, a plurality of scan lines S1, S2, . . . , Sn−1, and Sn arranged in rows, a plurality of data lines D1, D2, . . . , Dm−1, and Dm arranged in columns, a plurality of pixel power lines VDD for supplying power to the plurality of pixels, and a power supply 12 for providing voltages (e.g., predetermined voltages) to the pixel power lines VDD.
The image display unit 10 applies the scan signals transmitted from the scan lines S1, S2, . . . , Sn−1, and Sn and the data signals transmitted from the data lines D1, D2, . . . , Dm−1, and Dm to the pixels. The pixel circuits included in the pixels generate currents corresponding to the data signals and transmit the generated currents to the light emitting elements to display an image.
In this case, a positive pixel-driving voltage from the power supply 12 (in the lower portion of the display, as illustrated in FIG. 1) having a uniform level is applied to the pixels 11 through the pixel power lines VDD. As illustrated in FIG. 1, some of the pixels 10 are further from the power supply 12 (for example, pixels in the upper portion of the display) for applying pixel-driving voltages than others (for instance, pixels in the lower portion). Therefore, due to a non-uniformity of line resistance in accordance with lengths of the pixel power lines VDD commonly coupled to the power supply 12, the magnitudes of the IR drops of the pixel-driving voltages supplied to the pixels 11 are different from each other.
That is, the magnitude of the IR drop of the pixel power lines VDD is smaller when the pixel is closer to the power supply 12, while the magnitude of the voltage drop of the pixel power line VDD increases the further the pixel is from the power supply 12.
Therefore, the conventional organic light emitting display has a shortcoming in that the amount of current delivered to a pixel 11 for the same data signal varies in accordance with the position of the pixel 11 due to the non-uniformity of the IR drop of the pixel power lines VDD. Consequently, emission brightness becomes non-uniform. Such a problem becomes serious as the size of a panel increases.